An example of the arrangement of a conventional substrate transport apparatus will be described with reference to FIGS. 7A and 7B. The conventional substrate transport apparatus includes an arm unit capable of transforming the rotary motion of a drive source into a rectilinear motion. The arm unit includes two substrate holders aligned vertically (in the Z-direction), which respectively serve as a first substrate holder 701 and a second substrate holder 702.
For example, the moment a predetermined process is completed in a specific process chamber while an unprocessed substrate is mounted on the second substrate holder 702, the substrate transport apparatus rotates toward the process chamber in order to recover the processed substrate. The first substrate holder 701 on which no substrate is mounted moves toward the process chamber (FIG. 7A), receives the processed substrate in the process chamber, and returns the first substrate holder 701 to the retracted position (FIG. 7B).
To prevent any problem that may occur when the next process is successively performed without reliably transporting the processed substrate, the conventional substrate transport apparatus uses a sensor to detect the presence/absence of a substrate before and after a substrate exchange operation. It is determined based on this detection result whether a substrate has been reliably transported to the process chamber. In recovering a processed substrate, first, the substrate transport apparatus uses a sensor to confirm whether no substrate is present on the substrate holder for substrate recovery, and moves the substrate holder toward the process chamber after it confirms that no substrate is present on this substrate holder (see PTL1 and PTL2).